Gamma-aminobutyric acid (GABA) is considered to be an effective treatment for strokes, heart disease, diabetes, menopausal disorders, and dementia, therefore it is an important compound that needs to be analyzed. Because of its structural properties, GABA can be analyzed with highly sensitivity and selectively using HPLC with fluorescence detection by derivatization with orthophthalaldehyde (OPA, which binds specifically to amino groups). This application note details a method for simultaneous analysis of GABA and 17 different amino acids.